Gitaly comparison tests: made non-blocking with a startup timeout
If, for some reason, Gitaly failed to start, the tests run was blocking in a nasty way, requiring SIGTERM to kill the process.
One common reason is to forget to activate rbenv. Another one seems to be a HDK Gitaly service to be running on the same system, that we may now be able to investigate comfortably.
This solves the problem with a timeout, defaulting to 5 seconds,
and further tweakable with the
Note: 2 seconds would be too short already on my workstation.